The nitrosation of NN′-dialkylthioureas

Abstract

The reaction between nitrous acid and NN′-dimethylthiourea and imidazolidine-2-thione (ethylenethiourea) involves a rapid, reversible initial nitrosation at sulphur, followed by a slower transfer of the nitroso group to the secondary amino group to form an N-nitrosothiourea. The kinetics exclude the possibility of the N-nitroso compound being formed by direct N-nitrosation and require the S-nitroso compound to be a precursor. The conversion of the S-nitrosoalkylthiourea into the N-nitroso product involves rate-determining proton loss to form an intermediate which is partitioned between steps involving reprotonation and transfer of the nitroso group from sulphur to nitrogen.